<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    body {
        display: flex;
    }

    canvas {
        border: 1px solid black;
        margin: auto;
        margin-top: 30px;
    }
</style>

<body>
    <canvas id="canvas" width="500" height="500"></canvas>
</body>
<script>
    var c = document.getElementById("canvas");
    var ctx = c.getContext("2d");
    ctx.fillStyle = "#FF0000";
    ctx.fillRect(80, 60, 350, 175);
</script>

</html>